I use fill to reduce the front chamber volume, and without fill, it's 40 liters. When the front chamber is 40 liters, response is similar to the LABhorn. It's fine that way, but by reducing the front chamber, the ripple is reduced. The magnet sets the limit of depth for the chamber, but volume reduction can be done by displacing some space in the front chamber using filler material or panels. It's pretty easy to get front chamber volume down to 30 liters, but going smaller than that requires more attention and difficult fill shapes.

See the comparison of response curves with various front chamber sizes:

12π basshorn subwoofer with 20 liters of front chamber volume12π basshorn subwoofer with 30 liters of front chamber volume12π basshorn subwoofer with 40 liters of front chamber volume